Septic shock arising from gram negative infections continues to be a serious clinical problem with high mortality rates and increasing incidence. Many of the pathophysiologic changes of gram negative sepsis are thought to be induced by lipopolysaccharides (LPS) released during bacteriolysis. The long range goal of this research is to define molecular mechanisms of LPS-cell interactions which lead to injury. Macrophages, in particular hepatic macrophages, are major targets for LPS, and the response of these cells to LPS is characterized by release of a number of products which could mediate injury of parenchymal cells. Recently we have demonstrated that a substantial portion of intravenously injected LPS is converted to LPS-HDL complexes which are avidly taken up by adrenocortical cells and concentrated in lipid droplets. Thus, adrenocortical function could be affected by LPS either indirectly or by circulating macrophage products (indirect pathway) or directly by internalization of the LPS (direct pathway). A number of clinical and experimental observations suggest that adrenocortical insufficiency may be a contributing factor in septic shock, and we have shown that responsiveness of explanted rabbit adrenocortical cells to ACTH is suppressed by exposure of the cells to LPS-HDL complexes or supernatants from LPS treated macrophages. The major objectives of these studies are to determine the mechanisms and the pathogenic suppression. We will first establish optimal conditions for generation of suppressive factor in vitro by LPS treated murine peritoneal exudate cells and rabbit hepatic macrophages followed by determination of the biochemical properties of the macrophage factor(s). Explanted rabbit adrenocortical cells and the murine Y-1 adrenocortical cell line will be used to study the kinetics and mechanisms of macrophage factor- or LPS-HDL-mediated suppression of steroidogenesis. Finally we will examine the pathogenic significance of the indirect and direct pathways of LPS induced adrenocortical suppression in vivo using isolated perfused liver and adrenal preparations and experimental animals.